Unable to add new site

Hi,

I’m using multisites and running 5 sites and they were working fine till yesterday.
But today when I tried to add new site it’s says 404 page not found page.

my site url is https://demo.webhuntinfotech.com/

.htaccess code is:

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

 #Added by HostingRaja Security team, Please do not edit below.
 #For Support contact [email protected]
 #Uninstall vulnarable plugins from your WordPress
 <Files *.php>
 	Order Deny,Allow
 	Deny from all
 </Files>
 <Files index.php>
 	Order Allow,Deny
 	Allow from all
 </Files>
 <Files wp-login.php>
 	Order Allow,Deny
 	Allow from all
 </Files>

wp-config code:

/* Multisite */
define( 'WP_ALLOW_MULTISITE', true );
define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', false);
define('DOMAIN_CURRENT_SITE', 'demo.webhuntinfotech.com');
define('PATH_CURRENT_SITE', '/');
define('SITE_ID_CURRENT_SITE', 1);
define('BLOG_ID_CURRENT_SITE', 1);

any help would be appreciate.
Thanks